A computer user often needs to interact with the computer, which may be realized using an interactive input device, such as a keyboard, a mouse, or a touch screen. However, there are limits in using these devices. For example, conventional touch screens usually are based on technologies such as, for example, capacitive sensing or electric-field sensing. Such technologies can only track objects, such as the user's fingers, near the screen (that is, a short operational range), and cannot recognize the objects' 3D structure. Moreover, touch screens are usually used in small computers such as table computers. For a larger computer, such as a desktop or a workstation, it is often not convenient for the user to reach to the screen.
Therefore, there is a need for a human-computer interactive input system that has a larger operational range, is accurate and fast to resolve fine objects, such as a user's fingers, and has the ability to track an object's 3D motion and interaction with a surface.